Question about printing and designing

Well i got this question, about wich I am thinking for a while now…

Let’s say I want to make a poster, using for example a photo and some text and stuff, and I want this poster to eb printed on A2 or bigger, what do I do? Can I just design the stuff in photoshop on let’s say a4 format, en get it printed on A2? because I don’t think you can design a poster on a2 format on your pc… So to symplify the question; how do you design a poster that will be printed on a2 or bigger? What settings do you use etc etc.

Thanks,

Bart-c